Looking for Johnson SMG Part's

[MarkF1969]

Bo,
I wonder if the Hex/Allen bolt is loose allowing space between the breach/firing pin area? On the diagram, 500 being the sleeve, 460-466 being the hex bolt, 470 the breach. Any extra space there would allow that blowback from the crimped ammo. I have often fired mine on land with no problems other than bending a spear on impact with an old tire. A fine coat of Vaseline on the spear serves to keep out corrosion with just enough stickiness to keep the spear from sliding away from the sleeve in the barrel while diving. The Vaseline in the breach and on the sleeves seems to help keep the sleeves from getting stuck and a little extra waterproofing.
Stephanie's info is in Scott's reply. Scott also mentioned 3d printed sleeves. The ones Doug made so far the sleeve completely disintegrated when fired. The correct 3d printed plastic medium is out there... just need to find it. The advantage of plastic is they float when you drop one while diving!

The information for Stephanie is on Scott's reply. The diagram shows 460-466 as an Allen/hex bolt. If this is loose, it could allow space and blowback from the crimped ammo. I have often fired mine on land with no problems other than bending a spear on impact with an old tire. Vaseline on the sleeves, in the breach and on the spear helps the sleeves from getting stuck and adds a little extra waterproofing. The Vaseline adds just enough stickiness to the barrel and keeps the spear from sliding away from the sleeve while diving. The sleeve colors match the standard colors created by the Ramset stud driver ammo companies. Used as an impact driver for bolts into concrete. Here in the US, the ammo is found at any local hardware store. The 3d plastic medium we used so far looked great, but disintegrated when fired. The correct medium is out there for 3d printing. Check that hex head bolt and the space. I believe tightness doesn't affect the rotation of the barrel.

 

[Bo123]

Bo,
I wonder if the Hex/Allen bolt is loose allowing space between the breach/firing pin area? On the diagram, 500 being the sleeve, 460-466 being the hex bolt, 470 the breach. Any extra space there would allow that blowback from the crimped ammo. I have often fired mine on land with no problems other than bending a spear on impact with an old tire. A fine coat of Vaseline on the spear serves to keep out corrosion with just enough stickiness to keep the spear from sliding away from the sleeve in the barrel while diving. The Vaseline in the breach and on the sleeves seems to help keep the sleeves from getting stuck and a little extra waterproofing.
Stephanie's info is in Scott's reply. Scott also mentioned 3d printed sleeves. The ones Doug made so far the sleeve completely disintegrated when fired. The correct 3d printed plastic medium is out there... just need to find it. The advantage of plastic is they float when you drop one while diving!

I concluded at some point that it was best to re set the breach clearance. Maybe I noticed that sometimes the hex bolt that goes in the centre of the rotating breach, the surface it sits on can become damaged, the shoulder internally. I had that just machined a touch to clean the surface up, and re set the breach clearance. ie where the grub screw is tighten up on the hex bolt, would have moved the indentation for the grub screw. (It’s been a couple of years since I had a good play so having to have a good think but this is an interesting topic, glad there are some other enthusiests)